1. Field of the Invention
The current invention relates to liquid crystal display (LCD) devices that use a backlight source for illuminating a displayed image. More particularly, the invention relates to dimming of the backlight source to reduce power consumption, and also to adjustment of LCD transmittance values or image intensity values to compensate for dimming of the backlight.
2. Background Information
Various liquid crystal display (LCD) devices use a lighting source to either project an image onto a display surface such as a screen or have the light source positioned behind the LCD panel for direct viewing of an image produced on the LCD panel. A desire to reduce power consumption and improve the contrast of images displayed by LCD technology has led to various techniques for dynamically varying the light intensity of the light source and/or backlight of such LCD devices. Typically such variations in intensity of the light source results in a net dimming of the displayed image below the light intensity at which it was intended to be viewed.
In order to overcome this problem various compensation techniques have been proposed for backlight dimming. Examples of various techniques are disclosed in U.S. Pat. No. 5,717,422 to Fergasson, U.S. Pat. No. 7,053,881 to Itoh, U.S. Pat. No. 7,176,878 to Lew et al and US 2007/0092139. U.S. Pat. No. 5,717,422 proposes a backlight dimming factor based on average brightness of the image signal and simple expansion of LCD transmittance resulting in truncation of high brightness values. U.S. Pat. No. 7,053,881 proposes a backlight dimming factor based on average and peak intensity values of the image signal without LCD compensation resulting in perceived dimming of the displayed image. U.S. Pat. No. 7,176,878 proposes a linear amplitude boost of the LCD signal to compensate for backlight dimming, but does not discuss dimming methods. Finally, US 2007/0092139 proposes a backlight dimming factor based on peak intensity values of the image signal and linear expansion of LCD transmittance resulting in truncation of high brightness values.